In-flight breakup

RAYTHEON KING AIR C90, MUNSON, FLA., JUNE 25, 1999–According to the NTSB, poor judgment killed a pilot and his passenger when their aircraft came apart in flight during a midmorning journey up the west coast of Florida. The NTSB’s final report cited probable cause as “the poor in-flight weather evaluation by the pilot-in-command and his operation of the airplane at an indicated airspeed greater than the design maneuvering speed (Va) in a thunderstorm contrary to the pilot’s operating handbook, resulting in an in-flight breakup. A contributing factor in the accident was the failure of the pilot obtain in-flight weather advisories with any air traffic control facility before encountering the adverse weather.”

The Part 135 charter flight originated in Tampa shortly after 0830, with a planned destination of Brookley Field Airport (BFM) in Mobile, Ala. According to the St. Petersburg AFSS, the pilot filed an IFR flight plan by telephone, and when the briefer questioned him if he had obtained a weather briefing, the pilot said he had not. The briefer launched into a description of the significant weather, including “heavier thunderstorms up in through there.”

“The pilot was advised of one area of thunderstorms at least 50 miles south of the Panama City area, into the Panama City area, with a heavy cell just north of Mariana. The pilot was advised the second area was located just around the Mobile area on the east side of the bay, most of it extending into [the] Gulf about 100 miles or more,” according to the NTSB’s report. When the briefer suggested the pilot pick up Pireps along the way, the pilot responded that the airplane was equipped with airborne radar.

The convective sigmet covering the route of flight showed an area of thunderstorms moving from 260 deg at 20 kt with tops above 45,000 ft. The Tallahassee weather radar depicted a thunderstorm with tops at 48,000 ft some 85 mi west-southwest of Tallahassee. Records show the pilot did not attempt to obtain Pireps during the flight.

After departing VFR and picking up his IFR clearance airborne, N3019W flew the first half hour of the flight without incident. At 0904:07 the Jacksonville controller working the King Air’s sector contacted the pilot, warning of areas of heavy precipitation from 30 mi south of Panama City extending 20 mi to the east. The pilot responded, “Roger 19W. It looks like on our radar here that if we go straight ahead we’ll be all right there.”

At 1004, after transiting the airspace of several approach facilities, Jacksonville Center cleared N3019W to start a descent into Mobile. The controller broadcast the issuance of a convective sigmet three minutes later. At 1009:03 the controller cleared N3019W to descend and maintain 11,000 ft and advised him to contact Pensacola Approach.

The pilot checked in with approach at 1011 and advised he was descending to 11,000 ft. Several standard communications followed and then the King Air was cleared direct to Brookley. At 1012:44 the pilot responded, “All right.” Just over a minute later a broadcast from an unknown source was heard: “Three thousand outta control and going down.” Another broadcast that was unintelligible came two seconds later, and the controllers heard no other transmissions.

The NTSB headquarters in Washington prepared a “recorded aircraft radar and trajectory study” showing the estimated altitudes and airspeeds during the last few moments of the King Air’s flight. Combining the projected altitudes and airspeeds with the transmission data provides an understanding about why the aircraft came apart in flight.

Between 1009:33 and 1012:03 the King Air averaged an approximate 2,500-fpm descent. At 1012:39 the pilot requested a deviation for weather. Between 1013:15 and 1014:14 the aircraft plummeted from 11,100 ft to 900 ft (the last radar return), an approximate 13,000-fpm descent. However, the report comes with a disclaimer that the results are only estimates: “One should be wary of using the results of these calculations to determine whether or not the aircraft exceeded its design speed or any other quantitative information.”

Both of the airplane’s wings were found separated just outboard of the nacelles, and the horizontal stabilizers and elevators snapped off as well. Severed aircraft pieces were found just east of the main wreckage. Neither the gear nor flaps were extended. Extensive research of the wreckage revealed nothing that would suggest a system failure before the breakup. Va in the King Air C90 is 169 kt. The NTSB estimates that the aircraft reached 265 kt at its fastest point.

Weather reports at the Whiting Field Naval Air Station-North Airport (Whiting NAS) showed visibility was five miles, ceiling 1,500 ft broken and 3,500 ft overcast. Observers noted cloud-to-ground lightning to the east and thunderstorms from the east through the south, moving southeast. Whiting is 12 nm southeast of the accident site.

The FAA records show the pilot held an ATP certificate for multi-engine land and a commercial certificate for single-engine land airplane. He had a current second-class medical. In August 1998 he passed the annual Part 135 flight test on the third attempt. He passed the oral portion of the test on the first try. In February 1999, he passed the Part 135 oral and instrument proficiency test without a problem.